Thermally insulating batt and composite

ABSTRACT

The present invention relates to a thermally insulating batt comprising: (i) 10 to 70% by weight staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers; (ii) 10 to 70% by weight staple fibers; and (ii) 5 to 30% by weight binding agent that can also be used in a thermally insulating composite suitable for use in exterior portions of residential and commercial buildings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermally insulating batt that can be used in a thermally insulated composite suitable for use in an exterior portion, such as a wall or roof, of residential and commercial buildings.

2. Description of the Related Art

A batt suitable for thermal insulation preferably contains staple fibers that are strong, small in diameter and pack together in an open or loose manner. Undrawn melt spun staple fibers have large diameters. Drawn melt spun staple fibers have smaller diameters and are strong but are difficult to open or to spread the fibers apart during carding resulting in non-uniformity issues. Melt blown fibers have small diameters but are weak and tend to pack together too tightly resulting in sub-optimum thermal insulation.

It would be desirable to have a thermally insulating batt that contains staple fibers that are strong, small in diameter and pack together in an open or loose manner.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention relates to a thermally insulating batt comprising: (i) 10 to 70% by weight of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers; (ii) 10 to 70% by weight of second staple fibers; and (iii) 5 to 30% by weight binding agent.

In another embodiment, the present invention relates to a thermally insulating composite comprising: (a) a thermally insulating batt comprising: (i) 10 to 70% by weight of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers, (ii) 10 to 70% by weight of second staple fibers and (iii) 5 to 30% by weight binding agent; and (b) a moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate on one surface of the thermally insulating batt.

In still another embodiment, the present invention relates to an exterior portion of a building comprising the aforementioned thermally insulating batt or thermally insulating composite.

DETAILED DESCRIPTION OF THE INVENTION Definition of Terms

The term “batt” as used herein means single or multiple sheets of fibers used in the production of a nonwoven.

The term “nonwoven” or “web” as used herein means a structure of individual fibers or threads that are positioned in a random manner to form a planar material without an identifiable pattern, as in a knitted fabric.

The term “plexifilamentary fibers” as used herein means a three-dimensional integral network or web of a multitude of thin, ribbon-like, film-fibril elements of random length and with a mean film thickness of less than about 4 microns and a median fibril width of less than about 25 microns. The average film-fibril cross sectional area if mathematically converted to a circular area would yield an effective diameter between about 1 micron and 25 microns. In plexifilamentary structures, the film-fibril elements intermittently unite and separate at irregular intervals in various places throughout the length, width and thickness of the structure to form a continuous three-dimensional network.

The term “polymer” as used herein, generally includes but is not limited to, homopolymers, copolymers (such as for example, block, graft, random and alternating copolymers), terpolymers, etc., and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic, and random symmetries.

The term “polyolefin” as used herein, is intended to mean any of a series of largely saturated polymeric hydrocarbons composed only of carbon and hydrogen. Typical polyolefins include, but are not limited to, polyethylene, polypropylene, polymethylpentene, and various combinations of the monomers ethylene, propylene, and methylpentene.

The term “polyethylene” as used herein is intended to encompass not only homopolymers of ethylene, but also copolymers wherein at least 85% of the recurring units are ethylene units such as copolymers of ethylene and alpha-olefins. Preferred polyethylenes include low-density polyethylene, linear low-density polyethylene, and linear high-density polyethylene. A preferred linear high-density polyethylene has an upper limit melting range of about 130° C. to 140° C., a density in the range of about 0.941 to 0.980 gram per cubic centimeter, and a melt index (as defined by ASTM D-1238-57T Condition E) of between 0.1 and 100, and preferably less than 4.

The term “polypropylene” as used herein is intended to embrace not only homopolymers of propylene but also copolymers where at least 85% of the recurring units are propylene units. Preferred polypropylene polymers include isotactic polypropylene and syndiotactic polypropylene.

DESCRIPTION

The present invention is directed to a thermally insulating batt comprising: (i) 10 to 70% by weight of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers, (ii) 10 to 70% by weight of second staple fibers and (iii) 5 to 30% by weight binding agent. Preferably, the present invention is directed to a thermally insulating batt comprising: (i) 25 to 60% by weight of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers; (ii) 25 to 60% by weight of second staple fibers; and (iii) 15 to 25% by weight binding agent.

The staple flash spun plexifilamentary fibers of the thermally insulating batt can be made according to the flash spinning process described in U.S. Pat. No. 7,744,989 to Marin et al., which is hereby incorporated by reference. The flash spinning process produces a flash spun web of plexifilamentary fibers. The plexifilamentary fibers can be unbonded or lightly bonded. The flash spun web of plexifilamentary fibers can then be cut to a length of at least about 2.5 cm to make the staple flash spun plexifilamentary fibers. The staple flash spun plexifilamentary fibers preferably have a surface area of at most 10 m²/g or a crush value of at least 1 mm/g and more preferably a surface area of at most 5 m²/g or a crush value of at least 1.5 mm/g. The staple flash spun plexifilamentary fibers can be made of polyolefin polymer, preferably polyethylene.

The staple melt spun fibrillated fibers can be made according to any general process known to those skilled in the art. For example, melt spun fibrillated fibers can be made by melt spinning bicomponent polymer fibers with fiber cross sections such as round pie shape with pie wedges of alternating polymers or islands in the sea with the islands made from one polymer and the sea made from another polymer. The melt spun bicomponent polymer fibers can then be cut to a length of at least about 2.5 cm to make staple melt spun unfibrillated fibers. The staple melt spun unfibrillated fibers are later converted into staple melt spun fibrillated fibers via a carding process. The staple melt spun fibrillated fibers can be made of polyolefin polymer, polyester polymer, polyamide polymer or mixtures thereof.

The staple fibers can be made according to any general process known to those skilled in the art. The staple fibers preferably are stiff to provide some support and loft to the batt. The staple fibers can be made of polyester polymer, preferably polyethylene terephthalate, polyolefin polymer, polyamide polymer or viscose rayon.

The binding agent comprises at least one polymeric component with a melting point below the melting point of the staple flash spun plexifilamentary fiber melting point and the staple fiber melting point. The binding agent can take the form of staple binder fibers or small particles. The staple binder fibers can comprise multiple polymeric components with (a) at least one polymeric component with a melting point below the melting point of the staple flash spun plexifilamentary fiber melting point or the staple melt spun fibrillated fiber melting point and the staple fiber melting point and occupying at least a portion of a surface of the staple binder fibers and (b) at least one polymeric component with a melting point above that of the melting point of the at least one polymeric component with a melting point below the melting point of the staple flash spun plexifilamentary fiber melting point or the staple melt spun fibrillated fiber melting point and the staple fiber melting point. A common example of this type of staple binder fiber is a bicomponent fiber wherein a low melting point polymer on at least a portion of the surface of the fiber melts and adheres to another fiber while a high melting point polymer does not melt keeping a portion of the fiber intact.

The staple flash spun plexifilamentary fibers or staple melt spun unfibrillated fibers, staple fibers and a binding agent are mixed and fed to a carding machine to form a carded web. The carding process splits the larger diameter staple flash spun plexifilamentary fibers into microfibers or splits the staple melt spun unfibrillated fibers into staple melt spun fibrillated fibers by breaking the fibers apart along the interfacial boundary between the different polymers. The carded web is fed, for example, onto a conveyor belt or apron to a crosslapper, where lapper aprons crosslap the carded web by traversing a carrier means such as an intermediate apron in a reciprocating motion, to produce a thermally insulating batt of fibers that are oriented primarily in the transverse direction. The number of laps used to form the thermally insulating batt depends upon variables such as the desired weight of the base layer, and the final weight of the thermally insulating batt. The thermally insulating batt is then, optionally, fed into an oven at a temperature that will activate the binding agent to adhere fibers together and impart strength to the batt.

The staple flash spun plexifilamentary fibers or staple melt spun unfibrillated fibers, staple fibers and a binding agent may optionally be mixed and pre-opened in a card opener (For example a Dell'orco Villani co/1500 machine.) The blend may then be fed through a chute feeder (such as disclosed in U.S. Pat. No. 3,981,047), garnet (with crosslapping), or air-lay equipment to make a thermally insulating batt. The thermally insulating batt may then optionally be fed into an oven at a temperature that will activate the binding agent to adhere fibers together and impart strength to the batt.

In one embodiment the thermally insulating batt of the invention has a thermal conductivity/basis weight ratio, at 0.0318 m thickness, of less than 7.5×10⁻⁵ (W/m·K)/(g/m²), preferably less than 6.0×10⁻⁵ (W/m·K)/(g/m²).

In another embodiment the present invention is directed to a thermally insulating composite comprising: (a) a thermally insulating batt comprising: (i) 10 to 70% by weight of first staple fibers that comprise staple flash spun plexifilamentary fibers, (ii) 10 to 70% by weight of second staple fibers, and (iii) 5 to 30% by weight binding agent; and (b) a moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate on one surface of the thermally insulating batt.

The moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate can be a nonwoven comprising flash spun plexifilamentary fibers. The substrate is moisture vapor permeable with a moisture vapor transmission rate preferably of at least 130 g/m²/24 hr, substantially liquid impermeable with a hydrostatic head preferably of at least 180 cm, and substantially air impermeable with a Gurley Hill porosity preferably of at least 1000 s. Flash spun plexifilamentary fibers can be made for example according to the process described in U.S. Pat. No. 3,081,519 to Blades et al., which is hereby incorporated by reference. A suitable example is Tyvek® Homewrap™.

One surface of the thermally insulating batt is adhered to the moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate via any method known to one of ordinary skill in the art. For example, the thermally insulating batt and the moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate can be adhered together by a spray-on adhesive.

Another embodiment of the present invention is an exterior portion, such as a wall or roof, of a building comprising the thermally insulating batt or the thermally insulating composite of the invention.

Test Methods

In the non-limiting Examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials.

Basis Weight was determined according to ASTM D-3776 and reported in g/m².

Thickness was obtained from the thermal resistance test and is reported in meters.

Surface Area of the plexifilamentary fiber was measured by the BET nitrogen absorption method of S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc., V. 60 p 309-319 (1938) and is reported as m²/g.

Crush Value was determined using the following procedure. Three plexifilamentary fiber strands of different sizes were manually pulled from an unbonded plexifilamentary web. The three samples weighed about one, two and three grams. The reported crush values are the averages of the values measured on the three samples. Each sample plexifilamentary strand was formed into a ball shape with minimum application of pressure to avoid crushing and the sample was then weighed in grams. A crush tester comprised of an acrylic sample holder and crusher was used to measure the crush value of each sample. The sample holder comprised a cylindrical section having an inner diameter of 2.22 inches (5.64 cm) and an outer diameter of 2.72 inches (6.91 cm). The center of the cylinder was located at the geometric center of a square base measuring 6.00 inches by 6.00 inches (15.24 cm by 15.24 cm). The crusher comprised a cylindrical plunger rod (diameter=0.75 inches (1.91 cm)) having a first disk-shaped face (the disk having a thickness of 0.25 inches (0.64 cm) and a diameter of 2.20 inches (5.59 cm)) located at one end of the plunger rod and a second disk on the plunger rod spaced back 1.50 inches (3.81 cm) from the first disk. The second disk also had a thickness of 0.25 inches (0.64 cm) and a diameter of 2.20 inches (5.59 cm). The disks were sized slightly smaller than the inner diameter of the cylindrical sample holder in order to allow air to escape from the sample during crushing. The plexifilamentary samples were placed, one at a time, in the sample holder and a thin piece of paper having a diameter of about 2.2 inches (5.59 cm) was placed on top of the plexifilamentary sample prior to crushing. The plunger rod was then inserted into the cylindrical sample holder such that the first disk-shaped face contacted the piece of paper. The second disk served to maintain the axis of the plunger rod in alignment with the axis of the cylindrical sample holder. Each plexifilamentary strand sample was crushed by placing a 2 lb (0.91 kg) weight on the plunger rod. The crush height (mm) was obtained by measuring the height of the sample from the bottom of the cylindrical sample holder to the bottom of the crusher. The plunger and weight were removed from the sample after approximately 2 minutes, leaving the piece of paper in place to facilitate measurement of the restored height of the sample. Each sample was allowed to recover approximately 2 minutes and the restored height (mm) of the sample was obtained by measuring the height of the paper from the center of each of the four sides of the sample holder and averaging the measurements. The crush value (mm/g) is calculated by subtracting the average crush height from the average restored height and dividing by the average of the weights of the samples. The crush value is a measure of how much the sample recovers its original size after being crushed, with higher values indicating greater recovery of original sample height.

Thermal Conductivity was determined according to ASTM C-518. The test sample or specimen is located between two flat plates in a heat flow meter, and the plates are maintained at known, but different, temperatures. As heat flows through the test sample from the hot side to the cold side, a heat flux transducer measures the amount of heat transferred and thermocouples measure the temperatures of each of the two plates (i.e., of the so-called hot and cold plates). Fourier heat flow relation is used to calculate thermal conductivity. The thermal conductivity is reported in W/m·K.

Thermal Resistance is calculated using measured thermal conductivity and the thickness of the sample. Thermal resistance was reported in units of m²·K/W.

Thermal Conductivity/Basis Weight ratio was calculated by dividing the thermal conductivity by the basis weight and was reported in units of (W/m·K)/(g/m²).

Moisture Vapor Transmission Rate (MVTR) was determined by ASTM E398-83 (the “LYSSY” method) and is based on a pressure gradient of 85% relative humidity (“wet space”) vs. 15% relative humidity (“dry space”). The LYSSY method measures the moisture diffusion rate for just a few minutes and under a constant humidity delta, which measured value, is then extrapolated over a 24 hour period. MVTR is reported in g/m²/24 hr

Hydrostatic Head (HH) was determined by ATTCC 127 and is a measure of the resistance of the sheet to penetration by liquid water under a static load. A 17.78 cm×17.78 cm sample is mounted in a SDL 18 Shirley Hydrostatic Head Tester (manufactured by Shirley Developments Limited, Stockport, England). Water is pumped against one side of a 102.6 cm section of the sample at a rate of 60+/−3 cm/min until three areas of the sample are penetrated by the water. The hydrostatic pressure is measured in inches, converted to SI units and reported in centimeters of water. The test generally follows ASTM D 583 (withdrawn from publication November, 1976).

Gurley-Hill Porosity was measured in accordance with TAPPI T-460 using a Lorentzen & Wettre Model 121D Densometer. This test measures the time of which 100 cubic centimeters of air is pushed through a one-inch diameter sample under a pressure of approximately 12.4 cm of water. The result is expressed in seconds and is usually referred to as Gurley Seconds.

EXAMPLES

Hereinafter the present invention will be described in more detail in the following examples and the resultant data presented in the Table.

Example 1

Example 1 represents a thermally insulating batt of the present invention. The staple flash spun plexifilamentary fibers of the thermally insulating batt were made by using the flash spinning technology as disclosed in U.S. Pat. No. 7,744,989 to Marin et al., which is hereby incorporated by reference. Plexifilamentary fibers were flash spun at a temperature of 205° C. from a 20 weight percent concentration of high density polyethylene having a melt index of 0.7 g/10 min (measured according to ASTM D-1238 at 190° C. and 2.16 kg load) in a spin agent of 60 weight percent normal pentane and 40 weight percent cyclopentane. The plexifilamentary fibers were unbonded. The plexifilamentary fibers were cut to a length of about 2.5 cm to make the staple flash spun plexifilamentary fibers. The staple flash spun plexifilamentary fibers had a surface area of 8 m²/g and a crush value of 1 mm/g.

Fifty (50) % of the staple flash spun plexifilamentary fibers were then mixed with 35% staple polyester fibers with a cut length of about 3 cm and 15% of a low melting bicomponent sheath/core binder fiber of a polyester copolymer as the sheath and polyethylene terephthalate as the core. The staple mixture was fed to a carding machine. The carding process split the larger diameter plexifilamentary fibers into microfibers and further produces a fibrous structure or carded web. The carded web was fed onto a conveyor belt or apron to a crosslapper, where lapper aprons crosslapped the carded web by traversing a carrier means such as an intermediate apron in a reciprocating motion for 13 laps, to produce a thermally insulating batt of fibers that are oriented primarily in the transverse direction. The resulting thermally insulating batt had a basis weight of 534 g/m², a thickness of 0.0318 m, a thermal conductivity of 0.036 W/m·K, a thermal resistance of 0.883 m²·K/W and a thermal conductivity/basis weight ratio of 6.7×10⁻⁵ (W/m·K)/(g/m²).

Example 2

Example 2 represents a thermally insulating composite of the present invention. The thermally insulating batt from Example 1 was used to prepare the thermally insulating composite. The moisture vapor permeable, substantially liquid impermeable, substantially air impermeable substrate used was Tyvek®Homewrap™ (available from the DuPont Company, Wilmington, Del.). The substrate was moisture vapor permeable with a moisture vapor transmission rate of 370 g/m²/24 hr, substantially liquid impermeable with a hydrostatic head of 250 cm, and substantially air impermeable with a Gurley Hill porosity of 1200 s. One surface of the thermally insulating batt was adhered to the Tyvek® Homewrap™ by a spray-on adhesive of 77 Multi-purpose (available from 3M, St. Paul, Minn.).

Example 3

Example 3 represents a thermally insulating batt of the present invention. The staple melt spun fibrillated fibers (T-502 Fiber Innovation Technology, Johnson City, Tenn.) were 6 DPF and 0.006 m long. 50% of the staple melt spun fibrillated fibers were then mixed with 35% staple polyester fibers with a cut length of about 3 cm and 15% of a low melting bicomponent sheath/core binder fiber of a polyester copolymer as the sheath and polyethylene terephthalate as the core. The staple mixture was fed to a carding machine. The carding process split the larger diameter melt spun fibrillated fibers into microfibers and further produced a fibrous structure or carded web. The carded web was fed onto a conveyor belt or apron to a crosslapper, where lapper aprons crosslapped the carded web by traversing a carrier means such as an intermediate apron in a reciprocating motion for 13 laps, to produce a thermally insulating batt of fibers that are oriented primarily in the transverse direction. The resulting thermally insulating batt had a basis weight of 646 g/m², a thickness of 0.0318 m, a thermal conductivity of 0.034 W/m·K, thermal resistance of 0.935 m²·K/W and a thermal conductivity/basis weight ratio of 5.3×10⁻⁵ (W/m·K)/(g/m²).

Comparative Example 1

85% of the staple polyester fibers with a cut length of about 3 cm were mixed with 15% of a low melting bicomponent sheath/core binder fiber of a polyester copolymer as the sheath and polyethylene terephthalate as the core. The staple mixture was fed to a carding machine. The carded web was fed onto a conveyor belt or apron to a crosslapper, where lapper aprons crosslapped the carded web by traversing a carrier means such as an intermediate apron in a reciprocating motion for 13 laps, to produce a thermally insulating batt of fibers that are oriented primarily in the transverse direction. The resulting thermally insulating batt had a basis weight of 528 g/m², a thickness of 0.0318 m, a thermal conductivity of 0.043 W/m·K a thermal resistance of 0.739 m²·K/W and a thermal conductivity/basis weight ratio of 8.1×10⁻⁵ (W m·K)/(g/m²).

TABLE Basis Thermal Thermal Thermal Cond./ Gurley Plexifilament Fibrillated Binder Staple Weight Cond. Resist. Basis Weight Hill HH MVTR Sample Fiber % Fiber % Fiber % Fiber % g/m² W/m · K m² · K/W (W/m · K)/(g/m²) sec cm g/m²/24 hr Example 1 50 15 35 534 0.036 0.883 6.7 × 10⁻⁵ Example 2 50 15 35 1200 250 370 Example 3 50 15 35 646 0.034 0.935 5.3 × 10⁻⁵ Comp. Ex 1 15 85 528 0.043 0.739 8.1 × 10⁻⁵ 

What is claimed is:
 1. A thermally insulating batt comprising: (i) 10 to 70% by weight of the total batt of a collection of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers or both; (ii) 10 to 70% by weight of the total batt of a collection of second staple fibers; and (iii) 5 to 30% by weight of the batt of binding agent.
 2. The thermally insulating batt of claim 1, wherein the first staple fibers are present at 25 to 60% by weight of the total batt, the second staple fibers are present at 25 to 60% by weight of the total batt, and the binding agent is present at from 15 to 25% by weight of the total batt.
 3. The thermally insulating batt of claim 2, wherein the first staple fibers are present at 35 to 60% by weight of the total batt, the second staple fibers are present at 35 to 60% by weight of the total batt.
 4. The thermally insulating batt of claim 1, wherein between 5 to 50% of the second staple fibers have a weight of less than 3.0 denier per filament.
 5. The thermally insulating batt of claim 1, wherein the staple flash spun plexifilamentary fibers have a surface area of 10 m²/g or less or a crush value of at least 1 mm/g or both.
 6. The thermally insulating batt of claim 5, wherein the surface area is less than 5 m²/g or the crush value is at least 1.5 mm/g or both.
 7. The thermally insulating batt of claim 1, wherein the staple flash spun plexifilamentary fibers comprise a polyolefin polymer.
 8. The thermally insulating batt of claim 7, wherein the polyolefin polymer is polyethylene.
 9. The thermally insulating batt of claim 1, wherein the staple melt spun fibrillated fibers comprise a polyolefin polymer, polyester polymer, polyamide polymer or mixtures thereof.
 10. The thermally insulating batt of claim 1, wherein the staple fibers comprise a polyester polymer, polyolefin polymer, polyamide polymer or viscose rayon.
 11. The thermally insulating batt of claim 10, wherein the polyester polymer is polyethylene terephthalate.
 12. The thermally insulating batt of claim 1, wherein first staple fiber comprises a thermoplastic polymer and the binding agent comprises at least one polymeric component with a melting point below the melting point of the thermoplastic polymer.
 13. The thermally insulating batt of claim 12, wherein the binding agent is in the form of staple binder fibers.
 14. The thermally insulating batt of claim 1, wherein the first staple fibers comprise a thermoplastic polymer and the binding agent is in the form of staple binder fibers that comprise multiple polymeric components with (a) a first polymeric component with a melting point below the melting point of the thermoplastic polymer and that occupies at least a portion of a surface of the staple binder fibers and (b) a second polymeric component with a melting point above that of the first polymeric component and with a melting point below that of the thermoplastic polymer.
 15. The thermally insulating batt of claim 1, wherein the thermally insulating batt has a thermal conductivity/basis weight ratio at 0.0318 meters thickness, of less than 7.5×10⁻⁵ (W/m·K)/(g/m²).
 16. A thermally insulating composite comprising: (a) a thermally insulating batt comprising: (i) 10 to 70% by weight of the total batt of a collection of first staple fibers that comprise staple flash spun plexifilamentary fibers or staple melt spun fibrillated fibers; (ii) 10 to 70% by weight of the total batt of a collection of second staple fibers; and (iii) 5 to 30% by weight of the batt of binding agent and (b) a substrate adjacent to one surface of the thermally insulating batt wherein the substrate has a Gurley Porosity between 250 and 5990 sec/100 cubic centimeters/inch² a moisture vapor transmission rate (MVTR) of between 250 and 1870 grams/meter²/24 hours and a hydrostatic head of between 200 and 400 centimeters of water.
 17. The thermally insulating composite of claim 16, wherein 5 to 50% of the staple fibers weigh less than 3.0 denier per filament.
 18. The thermally insulating composite of claim 16, wherein the thermally insulating batt has a thermal conductivity/basis weight ratio at 0.0318 m thickness, of less than 7.5×10⁻⁵ (W/m·K)/(g/m²).
 19. The thermally insulating composite of claim 16, wherein the substrate is a nonwoven comprising flash spun plexifilamentary fibers.
 20. An exterior portion of a building comprising the thermally insulating batt of claim
 1. 21. An exterior portion of a building comprising the thermally insulating composite of claim
 16. 